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Structural Geology and Tectonics of the Paleoproterozoic Rocks of the Mount Rushmore Quadrangle, Black Hills, South Dakota ______

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Structural Geology and Tectonics of the Paleoproterozoic Rocks of the Mount Rushmore Quadrangle, Black Hills, South Dakota ______ STRUCTURAL GEOLOGY AND TECTONICS OF THE PALEOPROTEROZOIC ROCKS OF THE MOUNT RUSHMORE QUADRANGLE, BLACK HILLS, SOUTH DAKOTA ______________________________________ A Dissertation presented to the Faculty of the Graduate School University of Missouri-Columbia ______________________________________ In Partial Fulfillment Of the Requirements for the Degree Doctor of Philosophy ______________________________________ By JOSEPH CHRISTOPHER HILL AUGUST 2006 Dr. Peter I. Nabelek, Advisor Dr. Robert L. Bauer, Co-Advisor To my son, Aidan Christopher You gave me the reason to persevere… And my wife, Kristin Leigh You gave me the strength. Nothing is so firmly believed as what we least know. - Michel de Montaigne ACKNOWLEDGEMENTS It has been a long, bumpy ride over a long, long road and yet somehow I have arrived at the end of it – definitely a different person from when I started. As Henri-Frédéric Amiel said: “All appears to change when we change.” I have learned a lot, been given the opportunity to receive an excellent education, and in the process learned a lot about myself. I didn’t enjoy every minute of it, I regret some of it, and I understand a little better now that it is all over why kismet chose this path. To paraphrase Thomas Jefferson, the harder I work the luckier I get. I have lots of people to thank for guiding me, pushing me, and suffering me. First I would like to thank the members of my committee: Drs. Glen Himmelberg (emeritus), Erik Loehr, Kevin Shelton, and Alan Whittington and especially my co-advisors Drs. Robert Bauer and Peter Nabelek. I’m sure we would all agree that we wouldn’t want to do it all over again. A big thanks to Linda Garrison and Marsha Huckabey for everything they do to keep the Geological Sciences department going. Thank you to the Dr. Tom Freeman for being such a positive influence on me and for offering such good advice. I would also like to thank all the great friends that I’ve had while at Mizzou and point out that Aaron Johnson, Damon Bassett, Tim Huff, and Cathy Zumsteg are the salt of the earth, and that Aaron and I are not allowed out with each other without supervision as our wives won’t post bail. I would like to thank Brian Fagnan for just being the “Dude” and for hanging out all those summers in the Black Hills, talking geology, drinking copious amounts of alcoholic beverages, and laughing a lot. I will see you at the 75th Sturgis rally. Drew and Rebecca ii Hilpert became our closest friends while here in Missouri and for no other reason than that, I think our time in Missouri was well spent. As I write this, I find I should attach another bibliography to this work of names of friends too numerous to mention, I hope you know who you are (Carolina, Chris, John, Angie, Eric, and the rest). I wish each and every one of you the very best. Finally, to my wife Kristin, you know I owe this to your love and patience. To us babe, and to the fulfillment of a promise. iii TABLE OF CONTENTS ACKNOWLEDGEMENTS ........................................................................................ ii LIST OF ILLUSTRATIONS...................................................................................... vi LIST OF TABLES .................................................................................................... x LIST OF PLATES .................................................................................................... xi ABSTRACT .............................................................................................................xii INTRODUCTION...................................................................................................... 1 Importance of the Mount Rushmore Quadrangle as a Proxy for Understanding the Tectonics of the Black Hills ............................................... 5 Research Objectives.......................................................................................... 9 Regional Geologic Setting................................................................................ 10 Archean Basement..................................................................................... 11 Paleoproterozoic Rocks.............................................................................. 13 ~2550 – 2480 Ma Rift Succession........................................................ 13 ~2015 – 1885 Ma Continental Slope-Rise Type Succession ............... 15 1715 Ma Harney Peak Granite ............................................................. 15 Deformation and Metamorphism ................................................................ 16 Tectonic Models ......................................................................................... 18 Unresolved Issues of Black Hills Geology........................................................ 20 Lithotectonic Units versus Stratigraphy ............................................................ 21 Problems with Stratigraphic Correlation ..................................................... 24 Previous Stratigraphic Correlations ............................................................ 26 Methodology..................................................................................................... 27 Previous Geologic Mapping ............................................................................. 28 STRUCTURAL RELATIONSHIPS AND DEFORMATIONAL HISTORY................ 29 Summary of Previous Structural Studies.......................................................... 30 Deformational Events and Features Considered in this Study......................... 37 Bedding, Primary Sedimentary Structures, and Compositional Variation........................................................................... 38 D1 Deformation ........................................................................................... 42 Foliation ................................................................................................ 43 Folds..................................................................................................... 44 D2 Deformation ........................................................................................... 47 Foliation ................................................................................................ 48 Variations in S2 and Related Structures Across the Study Area......................................................................................... 53 Folds..................................................................................................... 57 Lineations ............................................................................................. 59 Variation of D2 Deformation Features by Fault Block ........................... 63 Faults.................................................................................................... 65 Recognition of a Major Structural Discontinuity.......................................... 71 D3 Deformation ........................................................................................... 75 D4 Deformation ........................................................................................... 76 Foliation ................................................................................................ 77 Faulting................................................................................................. 79 D5 Deformation ........................................................................................... 80 Foliation ................................................................................................ 80 Folds..................................................................................................... 81 Summary of Deformational Events................................................................... 81 TECTONIC OVERVIEW AND OBLIQUE CONVERGENCE MODEL .................... 87 v Laurentian Assembly: Overview...................................................................... 89 Incongruities with Laurentian Assembly ........................................................... 90 Problems with”Trans-Hudson”.................................................................... 91 Exposure............................................................................................... 92 Geophysical Interpretation.................................................................... 93 Age and Character of “Trans-Hudson” Rocks ...................................... 97 Wyoming Province Orogenies .................................................................. 100 Transpressional Model for the Study Area ............................................... 101 Structural Discontinuity....................................................................... 102 Emplacement of the Harney Peak Granite ......................................... 104 40 39 M1 Porphyroblasts and Ar/ Ar Data................................................. 110 Overall Structural Pattern and “Cross Folds”...................................... 112 Application of the Transpressional Model to the Black Hills ..................... 114 Transpressional Model....................................................................... 115 Extrapolation to the Tectonics of the Wyoming Province ......................... 117 CONCLUSIONS ............................................................................................. 120 REFERENCES CITED................................................................................... 125 APPENDIX A: Lithostratigraphic Units ..........................................................
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